Preparation And Characterization Of Composite Photocatalytic Material TiO₂/SiO₂/γ-Fe₂O₃ And Its Photocatalytic Properties

TiO₂ semiconductor photocatalytic oxidation is a new-style pollution treating approach in degradating dyeing waste water, whose virtues are high treatment efficiency, simple technics equipment, operating condition controlling easily, no toxicity, low price and chemical stability, etc. It is very expensive to use artificial UV light as source in traditional TiO₂ photocatalytic technology. This limits the application of photocatalytic technology in industrial.Meanwhile, the TiO₂ powder is difficult in the recovery and separation. And its active ingredients loss big. Therefore, the load of the TiO₂ catalysts for green materials, play an important role in wastewater treatment and air purification, etc, to meet the needs of sustainable development.The magnetic core was y-Fe2O₃ because of its good paramagnetism. y-Fe2O₃ was coated on the titanium dioxide surface directly via sol-gel technology. In this study SiO₂ layer as isolation between y-Fe2O₃ layer and TiO₂ layer, prepared composite photocatalytic material TiO₂/SiO₂/y-Fe2O3.Overcome the defect of partial oxidation of magnetic core, the interaction between titanium dioxide and the core was reduced during the heat treatment process. The optical, physical, chemical properties of TiO₂/SiO₂/y-Fe2O3 were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), standard electronic modules (SEM) and vibrating sample magnetometer (VSM). XRD patterns show that the diffraction peaks of TiO₂ are agree with the characteristic peaks of anatase TiO₂ in standard line to ensure the efficiency of the catalyst. UV-visible spectrophotometer results show that the intensity of light absorption of TiO₂/Si₂/y-Fe2O3 has increased not only in the UV region, but also in visible light range.This directly leads the improving of light utilization. The magnetic photocatalyst particles were easily separated and recovered using magnetic separation.The photocatalytic activities of the catalysts were measured by the model photodegradation of methylene blue (MB) under UV irradiation and visible light. The influence of various parameters, such as the content of ferrite loaded on TiO₂, catalyst dosage, the initial MB concentration and pH value, were mainly discussed. A number of single-factor experiments were done under different conditions. According to the results orthogonal table was made, the experimental results show that:the MB was degraded effectively to 98.8% by TiO₂/SiO₂/γ-Fe₂O₃ within 4 h under the conditions that the content of the SiO₂/y-Fe2O3 in catalyst was 20%,initial concentration of MB was 10 mg/L, pH was 9.7 and the content of catalyst was 1.0 g/L. The photocatalytic reaction under visible light is consistent with the UV irradiation.In the recovery experiments under UV irradiation, TiO₂/SiO₂/y-Fe2O3 catalyst still had high activity after using three times for the degradation of methylene blue solution. Degradation rate remained at 95%,and recovery rate of catalyst nearly at 96%.In the determination experiment of COD_Cr of methylene blue solution,4 h after the photocatalytic reaction, the removal rate of CODCr was 66.2%. Indicated that the mineralization of methylene blue by TiO₂/SiO₂/y-Fe2O3 catalyst was obvious. In the recovery experiments under visible light, TiO₂/SiO₂/y-Fe2O3 catalyst on the degradation rate of methylene blue up to 60% used for the first time. The removal rate of COD_Cr only reach 32.4%.Mineralization is not satisfactory. Biological treatment is needed inorder to meet higher standards.